Update lifecycle hooks snippets

[RusinovAnton]

2 new lifecycle hooks were added, componentWill- hooks been deprecated
in React 16.3

refs: https://github.com/facebook/react/releases/tag/v16.3.0

closes #40

[RusinovAnton]

@xabikos

Also we might want to add part with condition for getSnapshotBeforeUpdate() from example from react docs:

if (${1:condition}) {
  return ${2:snapshot};
}

return null;

refs: https://reactjs.org/docs/react-component.html#getsnapshotbeforeupdate

[RusinovAnton]

Deprecation note could definitely use some critique.

[xabikos]

@RusinovAnton thank you very much for the PR. I would happily merge it. But could you push another commit that removes the not needed white space? I would prefer to only see additions on this PR.

[RusinovAnton]

@xabikos done along with some fixes and additions